Which Observer Hears the Lowest Frequency?

Similarly, the observer on the left receives a longer wavelength, and hence he hears a lower frequency. The same thing happens in case (c). A higher frequency is received by the observer moving toward the source, and a lower frequency is received by an observer moving away from the source.

At what position will you hear the highest frequency?

The highest frequency of sound will be heard at position C, while the child is swinging forward. Assuming the child is moving with SHM, then the highest speed is at the equilibrium point, point C. And to have an increased pitch, the relative motion of the source and detector must be towards each other.

What is the change in the observed frequency called?

The Doppler effect describes the change in the observed frequency of a wave when there is relative motion between the wave source and the observer.